The invention relates to a thin film coil spirally wound, a method of forming a thin film coil, a thin film magnetic head including a thin film coil, and a method of manufacturing a thin film magnetic head.
Recently, improvement in performance of a thin film magnetic head has been sought in accordance with an increase in a surface recording density of a magnetic recording medium (hereinafter referred to simply as a “recording medium”), such as a hard disk. Widely used as the thin film magnetic head is, for example, a combined thin film magnetic head comprising a combination of a recording head having an inductive magnetic transducer for use in recording and a reproducing head having a magnetoresistive element for use in reproducing. The recording head is provided with a thin film coil which generates a magnetic flux to record data on the recording medium, and the thin film coil is one determinant factor of a magnetic path length closely related to the performance of the recording head. The magnetic path length corresponds to the length between a surface of the thin film magnetic head to be faced with the recording medium (hereinafter, the surface is referred to as an “air bearing surface”) and the position at which there are coupled two magnetic layers which are disposed with the thin film coil in between and each contain a magnetic pole. It is generally required that the magnetic path length be short. The reason is as follows. A short magnetic path length allows improvement in characteristics such as the flux rise time and nonlinear transition shift (NLTS), thus achieving improvement in the performance of the recording head. On the other hand, the thin film coil is required to exhibit lower electrical resistance.
General methods of forming such a thin film coil include a method utilizing photolithographic technique (see Japanese Unexamined Patent Application Publication No. 2001-60307, for example). Specifically, this method involves the following procedure. First, a substrate having a metal underlayer film formed thereon is coated with a photoresist film, on which a spiral resist pattern is then formed by use of photolithography. Then, a spiral conductive film is formed by means of plating using the metal underlayer film so as to fill a region between windings in the spiral resist pattern. Then, after the removal of the resist pattern, the metal underlayer film is removed by use of ion milling or the like, and an exposed gap in the conductive film is filled with an organic insulator such as a resist or an inorganic insulator such as aluminum oxide. The thin film coil is completed through the above-described procedure.
However, the method disclosed in the above patent literature 1 has difficulty in coping with a recent increase in the surface recording density. More specifically, an increase in the surface recording density of the recording medium requires that the recording head be of a minute size, and also requires that the thin film coil be formed within a very limited region (that is, within the width of stack as viewed in the in-plane direction of stack or within the thickness of stack as viewed in the direction of stack). In this case, the thin film coil is also required to exhibit lower electrical resistance, and therefore the thin film coil needs a small pitch of adjacent windings (that is, a narrow width of the region between windings), while ensuring that each winding (or turn) of the thin film coil has a certain width (or cross-sectional area). Thus, when the method disclosed in Japanese Unexamined Patent Application Publication No. 2001-60307 is used, the resist pattern must be formed so that its spiral portion has a smaller width. However, such a smaller width causes the resist pattern to deform or peel off in the spiral portion thereof, or causes the metal underlayer film to remain or be otherwise affected. Consequently, the above method has difficulty in reducing the width of the region between windings of the thin film coil. Thus, there has been also proposed a thin film coil having a double layer structure which ensures the cross-sectional area of each winding. However, this structure has the problem of causing an increase in the thickness of stack as viewed in the direction of stack.
Methods to solve this problem include, for example, a method which involves forming a first coil, then forming an insulating film on surfaces of the first coil (that is, the top and side surfaces thereof) and a bottom surface of a region between windings of the first coil, and then forming a second coil in the region between windings of the first coil, which is disclosed (in Japanese Unexamined Patent Application Publication No. 2002-343639, for instance). With this method, a thin film coil comprises a series of the first and second coils which are connected so that one end of the first coil is connected to one end of the second coil. The method disclosed in Japanese Unexamined Patent Application Publication No. 2002-343639 can be used to manufacture the thin film coil comprising the first and second coils which are formed in one plane at relatively high densities with the insulating film in between.
However, the method disclosed in Japanese Unexamined Patent Application Publication No. 2002-343639 has the problem that the side surfaces of the first coil may not be sufficiently covered with the insulating film. There is a strong tendency for this problem to arise, in particular when sputtering, evaporation or the like is used to deposit the insulating film on the surfaces of the first coil. For example when sputtering is used for deposition, it is necessary to appropriately set various conditions such as the degree of vacuum at which sputtering takes place, a sputter deposition rate, and the distance between a target and a substrate, and moreover the insulating film may partially have an insufficient thickness due to uncertainties such as variations in surface properties of the first coil and non-uniformity in the tilt angles of the side surfaces of the first coil. At the stage after the formation of the insulating film, it is also difficult to see whether or not the insulating film has a sufficient thickness. This may cause insufficient electrical insulation between the windings of the first and second coils and thus result in an electrical short circuit.